Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, a conventional magnetic tunneling junction (MTJ) may be used in a conventional STT-MRAM. The conventional MTJ includes a conventional pinned layer, a conventional free layer and a conventional tunneling barrier layer between the conventional pinned and free layers. The conventional MTJ typically resides on a substrate and may include conventional seed and capping layer(s) as well as a conventional antiferromagnetic (AFM) layer. A bottom contact below the conventional MTJ and a top contact on the conventional MTJ may be used to drive current through the conventional MTJ in a current-perpendicular-to-plane (CPP) direction.
The conventional pinned layer and the conventional free layer are magnetic. The magnetization of the conventional pinned layer is fixed, or pinned, in a particular direction. The conventional free layer has a changeable magnetization. The conventional free layer and the conventional pinned layer may each be a single layer or include multiple layers. The pinned layer and free layer may have their magnetizations oriented perpendicular to the plane of the layers (perpendicular-to-plane) or in the plane of the layers (in-plane).
To switch the magnetization of the conventional free layer, a current is driven perpendicular to plane. When a sufficient current is driven from the top contact to the bottom contact, the magnetization of the conventional free layer may switch to be parallel to the magnetization of a conventional bottom pinned layer. When a sufficient current is driven from the bottom contact to the top contact, the magnetization of the free layer may switch to be antiparallel to that of the bottom pinned layer. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the conventional MTJ.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. Mechanisms for improving the performance of STT-MRAM and for reducing the size of the magnetic junction are desired. However, a reduction in the lateral dimensions of the free layer may exhibit reduced thermal stability and an increased distribution in the minimum write current (or critical current density, Jc), the thermal stability constant Δ, coercivity (Hc), magnetic anisotropy (Hk), shift field experienced (Hshift) and/or other magnetic properties. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories. The method and system described herein address such a need.